1. Technical Field
The present disclosure relates to a mounting structure including a circuit board and a Ball Grid Array (BGA) connected to the circuit board, and a BGA ball.
2. Description of the Related Art
Recently, electric control of an automobile has progressed, and thus multiple electronic devices have been mounted on the automobile, and the number of electronic devices has been increased. Accordingly, it is difficult to sufficiently ensure a mounting space for the electronic devices to be mounted on the automobile, and thus the devices are required to be downsized. Therefore, a circuit board has been highly integrated in order to mount a plurality of electronic components having various functions on one circuit board.
According to the highly integrated mounting on the circuit board, integrated circuit components have also been highly integrated. In the related art, in the electronic device to be mounted on the automobile, a Quad Flat Package (QFP) in which terminals are arranged on four sides of the integrated circuit component or the like is mainly adopted. However, the QFP has been restrictively replaced with a BGA according to an increase in the number of signals from the integrated circuit component. The BGA is one type of package of the integrated circuit component to be mounted mainly on the circuit board in a Surface Mount Technology (SMT) method. In the BGA, electrodes are disposed on a bottom surface of the integrated circuit component in a lattice-shaped pattern. For this reason, the BGA is able to derive more signals than that of the QFP or the like. In the BGA, BGA balls which are spherical solder members are mounted on the electrodes disposed on the package bottom portion in the lattice-shaped pattern. In general, a BGA electrode and a circuit board electrode are soldered as follows.
FIG. 5 is a diagram illustrating a soldering sequence of the BGA electrode and the circuit board electrode. First, a solder paste which is a mixture of a solder powder containing Sn as a main component and a flux is supplied onto circuit board electrode 106 disposed on substrate 105 of circuit board 104 in advance by screen printing, and thus solder paste layer 110 is formed. BGA 108 includes BGA substrate 102, BGA electrode 103 formed on BGA substrate 102, and BGA ball 101 soldered onto BGA electrode 103 in advance. Then, BGA 108 is mounted on solder paste layer 110 such that BGA ball 101 is in contact with solder paste layer 110.
Thereafter, solder paste layer 110 is heated to the melting point thereof through an arbitrary method using hot air, an infrared ray, or the like, and thus solder paste layer 110 and BGA ball 101 are melted. Then, solder paste layer 110 and BGA ball 101 are cooled and solidified, and thus solder joining portion 107 and reacted layer 109 are formed. Accordingly, BGA electrode 103 and circuit board electrode 106 are joined through solder joining portion 107 and reacted layer 109.
As a mounting structure of the related art, a mounting structure has been known in which a BGA and a circuit board are joined by using a BGA ball having a ratio of Cu in Sn—Ag—Cu-based solder or Sn—Ag—Cu—In-based solder of equal to or greater than 3 mass % (for example, refer to Japanese Patent No. 4939891).